The research proposed herein seeks an understanding of the most peripheral components of eye movement control: 1) Extraocular motoneuron; 2) extraocular muscle; 3) extraocular proprioceptors. These three peripheral components will be studied under natural conditions of stimulation. Three main sets of experiments are proposed: 1) Evaluation of composite synaptic potentials recorded from extraocular motoneurons of rabbit during vestibuloocular reflex activation. Intracellular measurements would specify the form of the synaptic potential producing saccadic discharges. 2) Relationship of muscle fiber type to the control of force in extraocular muscle. The superior rectus muscle of the rabbit will be divided into an orbital layer, and a deep layer. The isometric tension of each layer will be measured and the recruitment of individual muscle fibers in each layer will be measured electrophysiologically during vestibular stimulation. We will examine the idea that: small diameter extraocular muscle fibers are the dominant elements of control when the eye is in primary position. 3) Two hypotheses concerning the possible role of extraocular proprioceptors in motor control will be tested: a) the phase of proprioceptive feedback is compared at a premotoneuronal level with a central command, and if the feedback is phased properly, it combines with a diminished central command to generate the signal guiding the movement. This notion views the primary role of proprioception in extraocular muscle as a substitute for signals of central origin during repetitive motor acts, and it will be tested by examining perturbations in the vestibuloocular reflex of one eye caused by externally induced changes in length of extraocular muscles. b) Feedback from extraocular proprioceptors is used to coordinate head position with eye position. This idea will be evaluated using monkeys as subjects by perturbing the position of one eye and recording changes in head position.